This really depends upon what ROM you currently are using. If you are updating from the previous aospCM7 release, you can skip wiping.
However, I have found issues doing it this way. It may be more tedious, but I suggest you ALWAYS wipe your caches before flashing a new ROM.
For example, I did not wipe when I switched to the latest release. No issues for a few days, then I tried using my camera, and FCs left and right. So I went back in, wiped the caches, and no problems since.
Use Titanium backup before you wipe, and you'll have a much easier time setting up your apps once finished, just install Titanium from the market, then use it to reinstall your apps with data.